This invention relates to sample cup assemblies for use in spectroscopic analysis, and more particularly, to a sample cup assembly having a sample cup centering system that enables the assembly to be utilized without an adapter in a conventionally sized sample cup holder of a spectroscopic instrument.
Spectroscopic techniques are commonly used for analyzing various materials. Such techniques rely on the changes that take place in the atoms and molecules of a material when electromagnetic radiation is absorbed or emitted thereby. Technological advancements in both wavelength-dispersive (WD-XRF) and energy-dispersive (ED-XRF) X-ray fluorescence instrumentation enable spectroscopic analysis of virtually all types of materials.
Sample cups of various well known designs are used in spectroscopic techniques to hold or contain liquid, solid and powdered specimens. Many of these sample cups consist of at least three components: a cup-shaped main cell; a thin film of material covering the open end of the cell; and a collar that pulls the thin film of material taut over the open end of the cell. The thin film of material operates as closure for the cup to retain the specimen to be spectroscopically analyzed within the cell, and as a sample surface plane that becomes exposed to an excitation source during the spectroscopic analysis. Such a sample cup is described in U.S. Pat. 5,451,375 entitled APPARATUS FOR TRIMLESS SAMPLE CUP USED IN X-RAY SPECTROSCOPY issued on Sep. 19, 1995 to Monte J. Solazzi.
Spectroscopic instruments typically come equipped with a non-removable sample cup holder of a fixed inner diameter. The bottom of holder includes an aperture for exposing the sample cup assembly to the instrument""s excitation source. Only sample cups assemblies with outer diameters complimentary to the inner diameter of the sample cup holder can be mounted therein such that the sample cup assembly is centered within the aperture of the holder. Sample cups assemblies with outer diameters that are significantly less than the inner diameter of the sample cup holder require adapters to center them with respect to the holder""s aperture. Improper centering of the sample cup assembly in the sample cup holder of the instrument can detrimentally alter the intensity of radiation impinging upon the specimen from the excitation source, thus causing the spectroscopic analysis to produce erroneous quantitative data.
Accordingly, there is a need for an inexpensive sample cup assembly which can be used in a conventionally sized sample cup holder of a spectroscopic instrument without the use of an adapter.
A sample cup assembly for use in retaining a specimen, comprising: a main cell for retaining the specimen, the main cell having an open end; a collar for locating a thin film over the open end of the main cell such that the film sealingly closes the open end of the main cell; and at least two projections extending from one of the main cell and collar for centering the sample cup assembly within a sample cup holder of a spectroscopic instrument.